The practice of inputting text to electronic devices, for example to form text documents or to send messages over communication networks has become generally widespread. Initially devices for inputting text were stationary and included large keyboards for inputting the text conveniently. In recent years the use of mobile devices has become more common and the size of the devices has been reduced significantly. Likewise the size of the keyboards for text input has been reduced.
As the size of the device has been reduced it has become desirable to reduce the size of the keyboard, for example by implementing a keyboard having a touch sensitive surface instead of mechanical keys. Commonly, the touch sensitive surface is combined with the display resulting in a touch screen that serves also for input and also for output. Typically, the device includes a display that is touch sensitive and a keyboard is virtually shown on the display. Users can select a key with their fingers by touching the display at the position in which the key is displayed. Due to the reduced size of the device some devices recommend using a pointing device such as a stylus or special pen to aid in accurately selecting keys.
Generally, when dealing with methods for inputting text into the device the issues of speed, accuracy and convenience need to be taken into consideration. Users are interested in quickly, comfortably and easily entering text without having to pause to assure accurate alignment to make sure that the keys are pressed exactly in the center.
In U.S. Pat. No. 7,453,439 to Kushler dated Nov. 18, 2008 there is described a method of using a touch sensitive keyboard for text input. In the disclosed method a user inputs words by forming contact with the keyboard using their finger or a stylus. The user forms contact with the touch sensitive keyboard by selecting the first letter of the word and then sliding from letter to letter in sequence to trace out all the letters of the word. The user only lifts the finger or stylus after the last letter. The intended word is determined based on the trace path also referred to as an input path. This method increases text input speed since:
1. The keyboard is constant so the user is accustomed to the positions of the letters;
2. The user's stylus or finger slides from letter to letter and does not need to be lifted, lowered, and positioned on each letter;
3. The letters do not need to be pressed accurately, rather it is sufficient to pass directly through the region defined for a key associated with the letter, and thus the user can move through the letters faster.
The method uses a word database to identify one or more words that best fit the input path. Generally the input path reflects a sequence of points that can each be associated with a key that may or may not participate in the word that was intended by the user. The disclosure suggests comparing the words from the database with the associated keys and determining the words that best fit the path. The disclosure specifies that the identification process is based on a number of important constraints, which must be followed, the constraints including:                1. Matching the first letter of the word with a “pen-down” action wherein the stylus first contacts the touch sensitive keyboard;        2. Matching the last letter of the word with a “pen-up” action wherein the stylus leaves the surface of the touch sensitive keyboard;        3. Matching the sequence of letters in the spelling of the word with the sequence of letters deduced from the input path.        
The above method was implemented in a product called Swype for use on mobile phones. The product was shown to indeed increase input speed and was demonstrated to set a Guinness world record regarding the speed for inputting a text message on a touch screen mobile phone.